DESCRIPTION (from abstract): Herpes simplex virus (HSV) keratitis is a leading cause of non-traumatic blindness in the US, with more than 200,000 cases per year. HSV can cause a variety of ocular diseases in humans ranging from self-limiting dendritic epithelial keratitis, conjunctivitis, and blepharitis to necrotizing stromal keratitis. In addition, HSV commonly causes cold sores, genital sores, and is a leading cause of viral encephalitis. The life cycles of HSV and other neurotropic herpesviruses are characterized by a lytic phase of infection at peripheral sites such as the cornea and skin during which all virus genes are expressed, and a latent phase of infection in neurons, during which gene expression is extremely limited. Latency represents a lifelong source of virus which can reactivate periodically causing severe ocular and other mucocutaneous damage, and the ability to establish lifelong latency renders HSV resistant to cure. One hallmark of the neurotropic herpesviruses is their ability to rapidly shut off macromolecular synthesis in the cells that they infect. It has been shown for HSV type 1 (HSV-1) that the gene responsible for this shut off is the product of the UL41 gene known as the virion host shutoff protein or vhs. Vhs is an important determinant of pathogenicity, allowing the virus to replicate to high titers in the cornea in vivo, to damage the cornea, and to establish latency with high efficiency. The objectives of this proposal are to investigate further the mechanisms of action and functions of the vhs protein in vivo. To this end, mutations will be introduced into the open reading frame of vhs as well as into other genes which are required for and associated with vhs activity. In addition, intertypic and interstrain recombinants will be generated in which vhs is exchanged from one virus to another. The effect of these mutations and exchanges upon the ability of the virus to induce degradation of host and viral mRNAs will then be measured by in vitro express/degradation assays and in vivo following introduction of these mutations into the context of the viral genome. Resulting mutants will also be tested for their ability to establish, maintain, and reactivate from viral latency in neurons. Efforts will also be made to assess the role of vhs in the induction of corneal damage and the role of interferons in limiting corneal disease. A better understanding of vhs will allow further insight into the mechanisms by which HSV can persist for the lifetime of its host and indicate novel therapeutic approaches and targets for control of this blinding disease.